1. Field of the Invention
The present invention relates to a photometer, and more particularly to a photometer improved by compensating for characteristic variations of a light receiving element due mainly to such environmental changes as temperature change.
2. Description of Prior Art
The conventional photometer uses a photomultiplier as a light receiving element, especially for the measurement of an extremely small quantity of light.
A photomultiplier is highly sensitive, but its characteristic variation is so large under the influence of temperature changes, etc. as to sometimes affect the measurement results. For this reason, in a photometer using a photomultiplier a standard light source is used for correction immediately before the purpose light is measured, thus eliminating or reducing the influence of characteristic variations on the measured light value.
It is cumbersome, in the above conventional photometer to carry out the correction step before the measurement as well as to provide the standard light source for correction as a means of eliminating or reducing the influence of environmental changes an the photomultiplier.
The standard light source generally consists of a gasfilled tungsten lamp, and it is difficult to maintain the high degree of measurement accuracy over a long term by using such a lamp which will inevitably deteriorate with the passage of time.